Considering the widespead use and intense national debate regarding the legal status of marijuana, new information regarding its actions deserves close scrutiny. The investigators have reported the development of gynecomastia following heavy human marijuana use in 16 patients. These developed tender breast masses after smoking marijuana at a time following their puberty. Careful history, physical examination, and in eight cases, laboratory testing has failed to reveal alternative causes of gynecomastia. This clinical experience has prompted us to initiate a laboratory investigation of the phenomenon of marijuana induced gynecomastia to determine the mechanism by which marijuana stimulates the breast. Initial studies have been performed and a model has been devised wherein rats are injected with delta 9 tetrahydrocannabinol (THC) over a three-week period, the breast tissue is excised, stained, and examined under dissecting microscope, and graded according to degree of breast development. Using this method, breast stimulation by delta 9 THC has been documented in multiple experiments. Further experiments will be necessary to refine this model, determine elutive potencies of the different cannabinoids, and to determine whether the action is directly on the breast or by release of pituitary or other hormones. No funds from this grant will be used on any studies of humans. The studies funded will be on rats.